This invention relates generally to semipermeable membranes and, more particularly, to a membrane made from a condensation polymer which has a molecular weight distribution that provides for enhanced physical properties and is particularly suited for use as an ultrafiltration membrane.
The term "ultrafiltration" as used in this application is intended to encompass microfiltration, nanofiltration, ultrafiltration, reverse osmosis and gas separation. Ultrafiltration may be performed using a variety of physical layouts which are well known to those skilled in the art and include both spiral wound and tubular modules.
Many applications of ultrafiltration technology involve food processing where sanitary conditions must be maintained at all times. This necessitates periodic cleaning with relatively harsh chemicals such as (by way of example only) chlorine containing compounds, other oxidizing agents, acids, alkalies and surfactants. These chemicals tend to degrade the membrane material and the ability of the membrane to withstand these chemicals is, in many cases, the determining factor in the useful life of the membrane.
Known materials for use in forming ultrafiltration membranes include many commercially available polymers such as polyether sulfone, polysulfone, polyarylether sulfones, polyvinylidene fluoride, polyvinyl chloride, polyketones, polyether ketones, polytetrafluoro ethylene, polypropylene and polyamides. The foregoing polymers differ widely in their physical properties and the particular material selected is based upon the properties necessary to support a particular use. While the higher molecular weight "chain" polymers such as polyvinyl chloride and polytetrafluoro ethylene exhibit superior resistance to degradation from cleaning chemicals, they also have undesirable attributes which eliminate them from consideration as membrane materials for certain applications. On the other hand, the lower molecular weight "condensation" polymers which exhibit certain desirable properties particularly suited for ultrafiltration applications are not as durable and have a short and unpredictable service life when exposed to the types of chemicals aforementioned.